A magnetic field generating device with low stray fields finds application in the design of a magnetic channel. A useful magnetic channel has a predetermined magnetic field generated in the channel by current sheets or current wires surrounding the channel. Such a channel is often used for the transport of particle beams. It is usually required that the channel have low stray fields so as not to disturb adjacent particle beams or instruments which are sensitive to magnetic fields.
One approach to the design involves a current structure creating a desired magnetic field in a specified area and having the concomitant stray field annihilated at larger radii by a system of coaxial currents completely surrounding said specified area.
Another approach to the design involves a septum magnet with a massive inner conducting core and an outer conducting shell. The shapes of the core and the shell may be selected in an iterative process using a computer algorithm which ensures zero stray field. Successive modifications of the shape may lead to satisfactory field in the channel. Then, the surface current is discretized in physically realizable current wires, introducing at the same time a small stray field. In order to generate the necessarily strong fields and to avoid the presence of any ferromagnetic material, superconducting current carriers have been suggested.